1. Technical Field
The present invention relates to exhaust gas recirculation (EGR) systems, and more particularly, to an EGR system having an active material actuated by-pass.
2. Discussion of Prior Art
Exhaust gas recirculation systems have been developed to reduce harmful emissions caused by internal combustion engines, and more particularly, to reduce NOx emissions from diesel engines. They function generally by recirculating at least a portion of the exhaust back to the engine, after cooling the portion through plural channels defined by an EGR cooler. Among the primary factors affecting their efficiency is EGR fouling (i.e., the accumulation of ash, and soot along the internal walls of the cooler). EGR fouling is of particular concern during engine start up, due to the propensity of large hydrocarbon particles to accumulate upon the cold or non-heated walls of the cooler. Fouling in turn contributes to other concerns, including increased emissions, compromised engine performance, and EGR failure caused by overheating due to the accumulated thermally resistive layer.
Various methods have been implemented to mitigate fouling, including manipulating the exhaust gas velocity, and using an oxidizing catalyst and/or filter; these measures, however, have presented various concerns, which limit their application and effectiveness. For example, it is appreciated that gas velocity manipulation is ineffective after sintering, and for nano-sized particles; and the addition of a catalyst and filter effects a substantial pressure drop that can influence engine performance. Most recently, a by-pass channel has been implemented to redirect the exhaust away from the EGR cooler during start-up; however, these measures rely upon sensors, associated electrical connections, and a power source to determine the engine temperature from the radiator coolant and manipulate the by-pass. As a result, they too present concerns relating to the added number of parts, and the costs, complexity, and packaging requirements associated therewith.